Toolbox items in Visual Studio 2010 are not persisting after closing VS and reopening

Question

I'm developing Windows Forms applications and using 3rd party controls(ex:Telerik). Whenever I want to add a new Telerik control to my form I have to do the following.

1. Add a new tab to the Toolbox and name it Telerik.
2. Add Items to the tab (all of the controls in the Telerik namespace)

Now, when I close VS2010 and reopen it, the toolbox items haven't persisted and I have to do it all over again.

This isn't a vendor specific question as it happens with any toolbox item I wish to add.

What gives?